Last week, I went to see Legally Blonde for fun, which it was. Particularly Sheridan Smith as Elle Woods, still giving 110% on a hot midweek evening six months into the run. But the most enjoyable aspect of the evening was the audience, who were all giving it 110%, too – despite the over-inflated seat prices, over-heated premises and £7 programmes.

Approaching the theatre we were met by a sea of young women dressed in shocking pink and, rather more bizarrely, a party of boy scouts. Once inside there were Mexican waves in the dress circle, and an engagement with what was happening on stage that was touching in its intensity. I'm certain that the woman behind me would have climbed on stage to biff Warner when he proposed to Vivienne if she had only been close enough.

The audience made the performance, and were an integral part of the experience – giving a lie to the thinking that any theatre that isn't immersive or interactive renders its audience passive. You only have to go to the Globe on any night of the summer, with the groundlings in the pit shouting and whooping and generally joining in, to see that isn't true.

The conditions in which critics most often see shows – on a press night, when there are few in the audience paying for their own seats – does everyone a disservice. Press nights are often strange, awkward affairs, with an atmosphere that more resembles a boxing match than a play. In one corner, the production's backers and supporters; in the other, the critics. The former frequently do more acting than the cast in demonstrating their rapture. In tiny venues such as the Bush, space is so limited that on press nights the audience can consist entirely of critics and the playwright's mum. Is that fair on the play? Or the playwright's mum?

Producers such as Legally Blonde's Sonia Friedman are starting to move away from the traditional press night, inviting critics to a choice of preview performances instead. Given that theatre is not just about what happens on stage, but also its audience, everyone is likely to benefit when the archaic practice of press nights is history.